The 7490 should not be used for a new design. It is a thoroughly dated part. You should find something similar in the 74HC/HCT series. However:
6 columns or rows of 4 LEDs each to display decades and unit values of hours, minutes and seconds in binary format. It will bend your mind to read the time. Use 6 of the 7490s, daisy-chained and driven by a 1Hz oscillator.
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